1. Field of the Invention
The field of the invention is techniques for pulling cables.
2. Background of the Invention
Contractile grips have been developed for pulling cable, such as mesh type pulling grips disclosed in U.S. Pat. No. 4,368,910. Such mesh type grips include a mesh of flexible wire loops which contract under tension, in a manner common to the well known "Chinese finger grip." The grips have been placed over the outer jacket of fiber optic cables in order to pull them over a distance through ducts or the like. Contractile cable pulling grips are constructed so that longitudinal tension forces reduce the diameter of the grip into a cable gripping position, while a longitudinal compression will increase the diameter, allowing the grip to be placed over or removed from a cable.
Even if cable strength members, such as aramid yarn, are tied directly to a loop on the pulling grip, a problem associated with such grips has been that, in general, fiber optic cables are designed to be pulled by their strength members, such as aramid yarns, and not by pulls on the outer jacket. In many cases, the outer jacket is not coupled directly to the strength members or other layers underneath the outer jacket, and this situation can result in creeping of the outer jacket relative to the underlying cable elements when a pull is performed.
Another problem with use of the mesh pulling grip according to previous methods is that if the yarn strength members of a fiber optic cable are tied to a loop on the pulling grip, aramid yarns can be so strong that the knotted aramid yarns tend to cut each other with certain knots. Major delays result if a knot breaks while the cable is being pulled through a duct.